Such a method and such a control unit are discussed in German patent document DE 195 36 110 A1. In this method, the setpoint value is determined from measured performance parameters of the diesel engine, an actual value is determined from signals of different sensors, and the actual value is regulated to the setpoint value in a closed loop. The manipulated variable for the regulation is activated at the beginning of a signal which triggers the injector for an injection. The beginning of this signal is referred to in the following as control start.
Basic values for the control start are stored for this purpose in a characteristics map, for example, which is addressed via performance parameters of the diesel engine. There is the so-called on-delay or dead time of the injector and the so-called ignition delay between the control start and the combustion start. The on-delay depends on the design of the injector and corresponds to a delay of the injector in responding to the control signal by starting an injection. The ignition delay is between this injection start and an actual beginning of the combustion, i.e., the combustion start. In the diesel engine, the combustion start is, as known, triggered by a self-ignition of the fuel injected into the combustion chamber charge heated by compression.
These influences may be taken into account when establishing the characteristics map values or by correcting the read-out values. The correction may take place by a regulation intervention or by linking to correction values determined as a function of performance parameters.
It has been found that in the known method, in particular at operating point transitions, uneven engine operation occurs.
In contrast, the method according to the present invention is characterized in that an ignition delay between the control start and the combustion start is estimated from performance parameters of the diesel engine using a computing model and the control start is formed from the setpoint value for the combustion start and the estimated ignition delay. The control unit according to the present invention is characterized in that it controls the sequence of such a method.